This application is based on Japanese Patent Application 2000-267576, filed on Sep. 4, 2000, the entire contents of which are incorporated herein by reference.
A) Field of the Invention
The present invention relates to a background noise eliminating apparatus and method suitable for eliminating background noise components from an impulse response waveform, and to a storage medium storing a program realizing such a method.
B) Description of the Related Art
An effector for generating sounds given a sound effect of an acoustic space such as a hall and a church is known, which effector records an impulse response waveform of the acoustic space and superposes a sample data sequence of the impulse response waveform upon sample data such as music sounds.
Sample data of an impulse response waveform of an acoustic space can be obtained by sampling an analog signal waveform of sounds in the acoustic space converted into an electric signal by a microphone. Sample data of an impulse response waveform is generally mixed with unnecessary background noise components in addition to main sounds.
The background noises are, for example, air conditioning sounds in a hall, illumination hums and the like picked up by a microphone.
As an effector gives a sound effect, background noise components contained in an impulse response waveform are superposed upon sample data such as music sounds. The sound effect initially intended by the effector cannot be obtained.
From the above reason, it is necessary to eliminate background noise components contained in an impulse response waveform. Conventionally, background noise components have been eliminated (or reduced) by the following two methods.
(First Method)
Two processes are repeated until background noises are eliminated. One process is to eliminate a signal in a frequency band assumed to contain background noises from an impulse response waveform by using an equalizer, and the other process is to reproduce sounds of the impulse response waveform and confirm whether background noises are still contained.
(Second Method)
Frequencies of an impulse response waveform are analyzed by fast Fourier transform (FFT). An operator identifies the frequency band containing background noise components from the analysis results, and selects a band elimination filter for removing the identified frequency band. By using the selected band-elimination filter, signal components in the frequency band assumed by the operator to contain background noise components are removed from the impulse response waveform.
The above-described background noise eliminating methods are, however, associated with the following problems.
(First Method)
An operator is forced to change or finely adjust the frequency characteristics of an impulse response waveform by operating an equalizer and to listen reproduced sounds to confirm the results. It takes, therefore, some time for the background noise eliminating work. Reproductivity is not possible because each operator may show different results of the background noise component eliminating work.
(Second Method)
An operator is forced to select a band-elimination filer and set various parameters necessary for filtering. Reproductivity is not possible because each operator may show different results of the background noise component eliminating work. In order to eliminate background noise components, frequency analysis by FFT and a filtering process are required so that the background noise component eliminating work is complicated and takes some labor.
It is an object of the present invention to provide a background noise eliminating apparatus and method capable of automatically deriving background noise components from an impulse response waveform and eliminating the background noise components, and to a storage medium storing a program realizing such a method.
According to one aspect of the present invention, there is provided a background noise eliminating apparatus, comprising: envelope detecting means for detecting an envelope of an impulse response waveform from a sample data sequence of the impulse response waveform; section detecting means for detecting a section during which a slope of the envelope detected by said envelope detecting means takes a value in a predetermined range including xe2x80x9c0xe2x80x9d during a predetermined time or longer; means for determining a background noise component value in accordance with sample data of the impulse response waveform during the section detected by said section detecting means; and background noise component eliminating means for reducing an absolute value of the sample data of the impulse response waveform by the background noise component value determined by said determining means.
Background noise components are automatically detected and removed from an impulse response waveform. A background noise component eliminating work can be automatically performed and a work time taken to eliminate background noise components can be shortened. The results of the background noise component eliminating works made by different operators are made uniform, and the reproductivity of the works can be maintained. The background noise component eliminating process can be realized with a simple structure.